Stockholders don't give a shit about console lifespan. They don't get a bonus if hardware hits any paritcular target like in year 6. They don't give a crap about that and they shouldn't really. It doesn't boost stock price, stock price is based on the current fiscal status of the company (that fiscal year namely). They want to see strong sales every fiscal year, not "well we shipped 20 million ... two fiscal years ago", the problem for Nintendo is by 2021/2022 they're going to have exhausted most of their franchise catalog, there will be likely by then at least 2 3D Marios, 2 3D Zeldas, 2 full blown Pokemon games + Pokemon Lets Go, etc.
Nintendo's business for many years has always gotten new hardware every 4-4 1/2 years, so any time a console or handheld was in the back half of its product cycle they always had a new console or handheld coming to refreshen the business cycle. So like for example when the GameCube was dying they had the Nintendo DS coming out while the GameCube was still relatively young (only 3 years old in Nov 2004), but that created a boost in yearly hardware shipments all the same. And when Wii was fizzling out, they had the 3DS come out when the Wii was only about 4 1/2 years old.
The staggered nature of the handheld and console hardware lines meant Nintendo enjoy a nice business shot in the arm quite regularly.
Stockholders don't care about handheld/console delineation, hardware shipments are hardware shipments and Nintendo gets their profit margin on any unit of hardware.
So I think that will be a challenge for them now that they only have one system, will stockholders and Nintendo's own business suits which have gotten used to the old model be "OK" with 2-3 years of shipments in the 8-12 million total hardware unit range. I'm not so sure they want to do that willingly (they were kinda forced to sustain themselves for a couple of years in that range because the Wii U flopped and 3DS was cratering in its back half, they had no choice because a new system wasn't ready ... but I doubt Nintendo willingly wants to ever go back to that level of hardware shipment again). That's one of the downsides of only having one hardware line.
